Ta/NiOx/Ni81Fe19/Ta films were prepared by rf reactive and dc magnetron sputtering. The exchange coupling field Hex and the coercivity Hc of NiOx/Ni81Fe19 as a function of the ratio of Ar to O2 during the deposition process were studied. The composition and the chemical states in the interface region of NiOx/NiFe were also investigated using X-ray photoelectron spectroscopy (XPS) and the peak decomposition technique. The results show that the ratio of Ar to O2 has a great effect on the chemical states of nickel in NiOx films. The exchange coupling field Hex and the coercivity Hc of Ta/NiOx/Ni81Fe19/Ta are thus seriously affected. XPS is shown to be a powerful tool for characterizing magnetic films.